Duchenne muscular dystrophy (DMD) is an X-linked recessive muscular disease resulting from mutation of dystrophin gene. It causes progressive myopathy of skeletal and cardiac muscle, leading to disability at early age and premature death of the patients. There is no effective treatment for DMD to date. Gene therapy has demonstrated its feasibility and promising potential in treatment for DMD. However, numerous obstacles remain before successful application of gene therapy to DMD patients. As most vectors have a limited packaging capacity for transgenes, the large size of the dystrophin gene (14 kb of cDNA) is one of the major hurdles in successful DMD gene therapy. We recently reported repair of the large size FVIII gene and the consequential hemophilia A phenotype correction by using a novel RNA repair strategy: splicesome- mediated RNA trans-splicing (SMaRT). Because SMaRT replaces only the mutated part of a gene, it obviates the need to deliver the entire cDNA of the gene, and therefore circumvents the potential inefficiency of delivering the large genes such as FVIII and dystrophin in a gene therapy vector. In addition, SMaRT corrects the endogenous mutated dystrophin gene, it thereby should induce minimal potential immunity against dystrophin following gene therapy. In this application, we propose to test SMaRT-based RNA repair for DMD gene therapy. Our long-term goal is to develop a successful gene therapy procedure for DMD. The objective of this proposal is to test feasibility and efficiency of SMaRT-based RNA repair in DMD gene therapy. The rationale underlying this project is that correction of mutant dystrophin gene and restoration of dystropin activity by SMaRT-based RNA repair will open a novel avenue to gene therapy for DMD, which also can be potentially applicable to other genetic diseases caused by defects in genes of large size. We propose two specific aims in this application: 1. To design and build dystrophin-specific Pre-Trans-splicing Molecules (PTM) that facilitate repair of the dystrophin mutation;2. To test feasibility and efficiency of SMaRT-based RNA repair in restoring dystrophin activity in a dystrophy transgenic mouse model (mdx4cv mice) following delivery of the dystrophin- specific PTMs by AAV vectors. PHS 398/2590 (Rev. 09/04) Page Continuation Format Page Principal Investigator/Program Director (Last, First, Middle): Chao, Hengjun Duchenne muscular dystrophy (DMD) is one of the most frequent genetic diseases. There is no effective treatment for DMD. The objective of this application is to test feasibility and efficiency of a novel gene therapy procedure for DMD. PHS 398/2590 (Rev. 09/04, Reissued 4/2006) Page Continuation Format Page